Power transfer management for local power sources of a grid-tied load

ABSTRACT

A power transfer system provides power factor conditioning of the generated power. Power is received from a local power source, converted to usable AC power, and the power factor is conditioned to a desired value. The desired value may be a power factor at or near unity, or the desired power factor may be in response to conditions of the power grid, a tariff established, and/or determinations made remotely to the local power source. Many sources and power transfer systems can be put together and controlled as a power source farm to deliver power to the grid having a specific power factor characteristic. The farm may be a grouping of multiple local customer premises. AC power can also be conditioned prior to use by an AC to DC power supply for more efficient DC power conversion.

RELATED APPLICATION INFORMATION

The present application is a divisional application from U.S. patentapplication Ser. No. 12/708,514, filed Feb. 18, 2010, and claims thebenefit of priority of that application.

Further, the present application is a non-provisional of U.S.Provisional Patent Application Ser. No. 61/153,940 filed Feb. 19, 2009,entitled “Power Transfer Management for Local Power Sources of aGrid-Tied Load”, and of U.S. Provisional Patent Application Ser. No.61/165,167 filed Mar. 31, 2009, entitled “Power Transfer Management forLocal Power Sources of a Grid-Tied Load”, and of U.S. Provisional PatentApplication Ser. No. 61/263,239 filed Nov. 20, 2009, entitled “Automaticand Remote Management of Power Factor in Grid-Tied Solar PhotovoltaicSystems”, and claims the benefit of priority of said applications.

FIELD

Embodiments of the invention relate to power conversion, and embodimentsof the invention more particularly relate to management of powertransfer from a local power source to a load that is tied to a utilitypower grid.

BACKGROUND

There have been many efforts over time to use local power sources tosupplement energy requirements from a utility power grid. Commonexamples include solar cells with photovoltaic (PV) inverters. Otherexamples may use wind energy, or another naturally occurring source,such as geothermal energy. Such sources are used in tandem with powerdrawn from a traditional power grid in the hope of reducing the power(and consequent cost) drawn from the grid. Such systems are designed todeliver power from the source to a load that includes both the localload and the power grid. Thus, from the perspective of the local sourcelooking out, traditional designs lump the local load and the grid as thetarget for power delivery from the system. Therefore, in practice suchsystems have always supplied both real and reactive power to the localload.

The power transfer from the local source to the local load is typicallyinefficient, resulting in the user wasting energy generated locally,which is then drawn from the grid. Thus, even where a local source maygenerate significant amounts of energy that would seemingly satisfy theneeds of the local load, the local load typically must also draw realand reactive power from the grid at measurable cost to the customer.

The tariff governing the cost of electricity to utility power gridcustomers depends upon many factors, including size of a customer's baseload, the time of day that the electricity is demanded, and the type ofpower demanded (whether it be active or reactive power). The tariffstructure requires the customer to pay more, for example, if the poweris used during peak demand hours, when the utility has little reserveavailable for emergencies, or, for example, if the type of power isactive, instead of reactive power. In general, residential customers donot pay for reactive power under current tariffs, whereas industrialcustomers do.

Reactive power is becoming more costly to the utilities to produce thanit once was, for several reasons. First, the demand for reactive poweris growing much faster than for active power, because many newelectronic and electrical products are requiring more reactive powerthan ever before. These products include plasma and LCD TVs, computerpower supplies, and grid-tie electrical vehicles. Second, reactive poweris more costly to transport down long distance transmission lines thanis active power, because it causes voltage drops approximately 10 timesgreater than does active power. Third, although reactive power can becompensated for on the local distribution lines, thereby canceling theneed to build larger generating stations many kilometers away, thecompensators are expensive to buy and maintain.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description includes discussion of figures havingillustrations given by way of example of implementations of embodimentsof the invention. The drawings should be understood by way of example,and not by way of limitation. As used herein, references to one or more“embodiments” are to be understood as describing a particular feature,structure, or characteristic included in at least one implementation ofthe invention. Thus, phrases such as “in one embodiment” or “in analternate embodiment” appearing herein describe various embodiments andimplementations of the invention, and do not necessarily all refer tothe same embodiment. However, they are also not necessarily mutuallyexclusive.

FIGS. 1-2 each illustrate a block diagram of an embodiment of a systemthat transfers power from a local source to a grid-tied load with powerfactor conditioning.

FIG. 3 is a flow diagram of an embodiment of a process for transferringpower from a local source to a grid-tied load with power factorconditioning.

FIG. 4 is a block diagram of an embodiment of a system with multiplepower sources, a power extractor, and multiple AC loads.

FIG. 5 is a block diagram of an embodiment of a system that controlsharmonic distortion with a software feedback control subsystem coupledto a hardware waveform controller.

FIG. 6 is a block diagram of an embodiment of a system that controlsharmonic distortion.

FIG. 7 is a block diagram of an embodiment of a system with multiplepower sources, a power extractor, and multiple loads.

FIG. 8 is a block diagram of an embodiment of a power extractor.

FIGS. 9-13 each illustrate a block diagram of an embodiment of anexample of power transfer circuitry.

FIG. 14 is a block diagram of an embodiment of cogeneration of powerfrom a local source and a utility grid to a grid load that neighbors thelocal source.

FIG. 15 is a block diagram of an embodiment of a power factor enhancedpower supply.

FIGS. 16A-B illustrate an embodiment of phase, active, and reactivepower that are controlled by power factor conditioning.

FIG. 17 is a block diagram of an embodiment of a system that controlspower factor at a local load.

FIG. 18 is a block diagram of an embodiment of a system that controlspower factor on a grid-facing connection by controlling power factor ata local load.

FIG. 19 is a block diagram of an embodiment of a system that controlspower factor at a grid connection by controlling power factor at a powersource farm.

FIG. 20 is a block diagram of an embodiment of a power factor feedbackmechanism.

FIG. 21 is a block diagram of an embodiment of a communication system tocontrol power factor remotely.

FIG. 22 is a block diagram of an embodiment of a system that controlspower factor with a master/slave configuration.

FIG. 23 is a block diagram of an embodiment of a control process forpower factor control.

Descriptions of certain details and implementations follow, including adescription of the figures, which may depict some or all of theembodiments described below, as well as discussing other potentialembodiments or implementations of the inventive concepts presentedherein. An overview of embodiments of the invention is provided below,followed by a more detailed description with reference to the drawings.

DETAILED DESCRIPTION

Real-time conditioning of power factor enables more efficient powertransfer from a local source to a grid-tied local load. Additionally,the power transfer from the source to the load is further improved withreduction of harmonic distortion in accordance with total harmonicdistortion control, and maximum power extraction from unstable andvariable energy sources with dynamic impedance matching. Current systemsthat use power from a local source do not condition the power factor ofthe generated power from the variable or unstable source. As usedherein, “metastable” refers to a source that may be unstable or variablein its production of power. Examples of such sources are solar arrays,windmills, or other “green” sources. As used herein, a “local” load anda “local” source are local with respect to each other. Local refers tobeing on the same electrical system with respect to each other, and morespecifically, being on the same side of a power grid point of connection(e.g., the “line in” from the grid that typically goes through a powermeter and breaker box). Local does not necessarily imply any specificgeographic requirements other than practical limitations for systemdesign that would be apparent to one skilled in the art.

In prior systems that attach metastable sources as power sources to agrid-tied (local) load (e.g., a house, apartment, cabin, or otherdwelling), power factor conditioning is not considered with respect tothe grid power. Power factor has not been considered significant to autility power consumer, but is rather a consideration of the powerutility and industrial consumers with large inductive machinery. Powerfactor correction for utility consumers, especially with respect topower generated from metastable sources, may not be considered because:a) impedance loads typically have been thought of as the controller ofpower factor, not the inverters that supply power to the load; and, b)in engineering models that consider power flow, the local load is notusually distinguished from the general load on the side of the utilitypower grid (looking out from the local source). Thus, maximizing powertransfer to the local load is not considered in engineering modelsconcerned with attaching metastable sources to the power grid.

However, considering the local load separately from the general load onthe side of the utility power grid, and controlling power transfer tothe local load, including conditioning power factor of the generatedpower and maximizing power transfer to the load can result in greatlyimproved power transfer efficiency. Additionally, as set forth in moredetail below, the use of power factor conditioning can result in havingonly real power supplied by the metastable source, and all reactivepower requirements are supplied by the grid. In certain circumstances,the grid may provide only reactive power, and no real power to the load.

FIG. 1 is a block diagram of an embodiment of a system that transferspower from a local source to a grid-tied load with power factorconditioning. System 100 represents a power system that includesmetastable source 110, inverter 120, load Z102, and utility power grid130. Load Z102 represents a consumer premises (e.g., a home) tied togrid 130. Metastable source 110 (e.g., solar cells/array, wind powergenerator, or other time-varying or green power source) and inverter 120are local to load Z102, and provide power to the load. Moreparticularly, metastable source 110 produces a variable/unstable sourceof DC power (shown as Psource, or source power). The source may betime-varying and/or change in available power due to environmentalconditions. Inverter 120 represents a dynamic power extractor andinverter apparatus.

Under normal operation, DC power is drawn from source 110, andextracted, inverted, and dynamically treated by inverter 120, todynamically produce maximum AC current relatively free of harmonicdistortion and variability, and completely in phase with the AC voltagesignal from power grid 130. Putting the generated AC current in phasewith the grid AC voltage produces AC power with a power factor at ornear unity to load Z102, meaning that all reactive power drawn by theload comes from grid 130. If source 110 produces enough energy tosatisfy the real power requirements of load Z102, the only AC powerdrawn from grid 130 by the load is, or nearly is, exclusively reactivepower. When source 110 is unable to produce DC power sufficient to servethe load, real power may also be drawn from the grid in the ordinaryfashion.

Alternatively, as described in more detail below, the AC current may beintentionally changed to be out of phase to a certain extent withrespect to the AC voltage signal of the grid. Thus, the single inverter120 can deliver power at any desired power factor to compensate forconditions of power on power grid 130.

The inverter current (Iinverter) and the grid current (Igrid) are shownpointed towards grid 130, illustrating the scenario where sufficientenergy is produced by source 110 to actually service Z102 with the loadcurrent (IL), and “give back” to the grid. Power can be given backgenerally to the grid, and the customer can be appropriately compensatedfor power provided to the grid. Additionally, a give back scenario caninvolve providing power to a neighbor customer, as described in moredetail below with respect to FIG. 14.

Grid 130 includes power meter 132, which measures the real powerconsumed by load Z102. Typically, the voltage and current are measured,and the power computed. Note that in the case where only reactive poweris drawn from the grid, power meter 132 will not measure any power usageby load Z102.

As discussed, in one embodiment, the power factor delivered by inverter120 to load Z102 is at or near 1.0 for introduction to the local loadand to the power grid. In addition to power factor correction, inverter120 provides harmonic distortion correction. In one embodiment, inverter120 provides table-based harmonic distortion correction. Previousharmonic distortion techniques use a hardware-based method or FastFourier Transform (FFT). The table-based method implemented on aprocessor or controller reduces cost per inverter and scales better thantypical hardware implementations.

In addition to causing a power factor near or at unity for powerdelivered from inverter 120, inverter also monitors the operatingconditions, and provides maximum power from the source 110 dynamicallyand in real time with changes in the energy source and current load.Thus, if the amount of energy generated by source 110 changes, inverter120 can modify the output based on that source in real time.Additionally, if the resistive conditions of load Z102 (e.g., aninductive motor such as a vacuum is turned on), power factor correctionautomatically tracks the needs of the load and adjusts to the real-timechanges in the load. Additionally, total harmonic distortion adjusts forharmonic distortion more efficiently than what is required by standards,thus complying with standards and improving performance of the system bydynamically adjusting to variable and unstable power sources, and to achanging load.

It will be understood that if the output voltage and current of inverter120 are matched in phase with each other and with the voltage on thegrid (e.g., through a phase lock loop, or through a power generationsampling and feedback mechanism), any reactive power necessary will beabsorbed from the grid. The more real power provided by source 110, thefurther out of phase the grid voltage and the grid current will belocally at Z102. If all real power is provided locally, the current andvoltage of the grid will be 90 degrees out of phase locally at loadZ102, causing the grid real power contribution to fall to 0 (recall thatPreal=(Vmax*Imax/2)cos(Vphase−Iphase)).

FIG. 2 is a block diagram of an embodiment of a system that transferspower from a local source to a grid-tied load with power factorconditioning. System 200 provides one example of system 100 of FIG. 1.Metastable source 210 is a variable or unstable power source. System 200includes inverter 220, which includes DC/DC converter 222, coupled toDC/AC inverter 224, both of which are coupled to and controlled bycontroller (CPU) 240. Additionally, switching device S226 (e.g., arelay) selectively connects the inverter to load Z202 and grid 230.

Controller 240 monitors the AC current, which moves out of DC/ACinverter 224, and the generated voltage of grid 230, which appearsacross load Z202. Controller 240 controls at least one parameter,parameter 242, of the operation of converter 222, and parameter 244, ofthe operation of inverter 224. Parameters 242 and/or 244 may be a dutycycle of a switching signal of the power extraction devices (see figuresbelow for further description). The modification of the parameter isdependent on the quality of the monitored current and voltage.Controller 240 further controls switching device S226 to couple the loadto power produced (by converter 222 and inverter 224 from source 210),when suitably conditioned power is available for use by the load.

In operation, controller 240 dynamically monitors the operation of thesystem to extract and produce AC current from source 210 at a selectedpower factor (e.g., fully in phase or at some other phase) with respectto the AC voltage provided by grid 230. When the current is sufficientlyconditioned and abundant for use with the load, the load and the gridare presented with the full maximum real power, meaning primarily oronly reactive power is drawn from the power grid. Because power meter232 registers only real power drawn from grid 230 by load Z202, and notreactive power, the real power drawn by the local load is not billed.

In one embodiment, utility power grid 230 includes var (volt-amperesreactive) meter 234 to monitor the use of vars by load Z202. The varsmay be monitored by performing measurements based on the phase of thecurrent and voltage of the grid power at the load, and performingcalculations based on the measured values.

In one embodiment, inverter 220 includes tables 250, which provides atable-based method for controlling power factor. The tables may includeentries that are obtained based on input conditions measured from thesystem, to achieve a desired power factor. Feedback from the grid-tiednode may include voltage zero crossing, voltage amplitude, and currentwaveform information. With such information, controller 240 uses tables250 to adjust the operation of converter 222 and/or inverter 224. Thetables may include setpoints that provide idealized output signals thesystem attempts to create. By matching output performance to anidealized representation of the input power, better system performanceis possible than simply attempting to filter and adjust the output intraditional ways.

While certain specific discussions are provided above with respect tosystems 100 and 200, in general, the systems may be further described bythe following. Metastable DC power is dynamically treated with anapparatus to produce maximum AC power at unity power factor and lowharmonic distortion. An apparatus could be provided having circuitry tocouple the metastable source to the load, such as connecting to theload's grid connection. The apparatus may include a DC/DC converter anda DC/AC converter (inverter) having at least one dynamically modifiableparameter (e.g., duty cycle of a switching control component, pulsetrain period of a pulse train used to construct a signal), controlled bya power generation controller.

The controller dynamically modifies the parameters to producelow-distortion AC current. In one embodiment, the AC current is entirelyin phase with the voltage provided by the grid, thus having a powerfactor near unity, so that all or most of the actual real powerrequirements are provided by the apparatus. Consequently, only or mostlyreactive power, if any, would be drawn from the grid. Such an approachmaximizes the benefit of treating the load with energy drawn from themetastable DC energy source, while minimizing the cost of drawing energyfrom the grid.

In one embodiment, the dynamic modification of the parameters isperformed with a table-based method for adaptively modifying theproduced AC current waveform to correct power-factor and to reduce totalharmonic distortion. Additionally, the energy transfer is maximized bythe use of a dynamic means to extract power, such as described in Besseret al., Multi Source, Multi-load Systems with a Power Extractor, U.S.Publication No. 2008/0122518 A1, and as described in more detail belowwith respect to FIG. 4.

FIG. 3 is a flow diagram of an embodiment of a process for transferringpower from a local source to a grid-tied load with power factorconditioning. Flow diagrams as illustrated herein provide examples ofsequences of various process actions. Although shown in a particularsequence or order, unless otherwise specified, the order of the actionscan be modified. Thus, the illustrated implementations should beunderstood only as an example, and the process for establishing thesecure channel can be performed in a different order, and some actionsmay be performed in parallel. Additionally, one or more actions can beomitted in various embodiments of the invention; thus, not all actionsare required in every implementation. Other process flows are possible.Additionally, it will be understood that not all operations illustratedand discussed are necessary in every embodiment—some operations may beoptional.

The operation of an apparatus as discussed above with respect to dynamicconditioning may be described nominally in four parts. In a first part(e.g., 302-308), the AC voltage created by the apparatus is conditionedto be fully in phase with the AC voltage of the utility power grid. Theconditioning brings the generated AC voltage into phase with the gridvoltage. In the second part (e.g., 310-314), one or more parameters ofthe converters are controlled until the AC current derived from theapparatus is conditioned to be in a desired phase with respect to the ACvoltage of the utility power grid (which is also in phase with thegenerated AC voltage). In one embodiment, the desired phase is fully inphase; thus, the power factor of the generated power is brought tounity. In the third part (e.g., 318-320), the one or more parameters canbe further controlled until the total harmonic distortion of the ACcurrent from the apparatus is reduced to a satisfactory level. In thefourth part (e.g., 322-326), the one or more parameters can becontrolled to extract and provide maximum real power from the DC powersource in a non-variable, constant manner.

In the first part, the voltage of the generated AC power is phase lockedto the phase of the voltage of the grid, 302. The source power isreceived, 304, and converted into AC voltage and current, 306. Thevoltage of the grid can be measured and the phase of the generated ACvoltage locked to the phase of the grid, 308. The AC voltage on theutility grid, across the local load, is periodically monitored by thecontroller, for example, with phase lock looping, and the one or moreparameters is modified, until the inverter AC voltage is in phase withthe power grid voltage.

In the second part, the power factor is conditioned, 310. The AC currentproduced by the inverter is monitored at a periodic interval rate, andthe grid voltage phase is detected, 312. In one embodiment, the periodicinterval rate of monitoring the AC current is performed not fewer than320 times per second. Dynamical modification of the inverter parameter,based on a table of pre-defined values, occurs until the alternating ACcurrent produced by the inverter is at, or nearly in phase with, theutility grid voltage across the load. Thus, the phase of the generatedAC current is locked to the grid voltage phase, 314.

In the third part, the AC current generated by the apparatus is furtherconditioned to reduce total harmonic distortion, 316. The output signalbeing generated is measured or sampled, 318, and the output signal isadjusted based on an ideal signal through table lookup, 320. Forexample, the controller may dynamically modify a table of sine-wavevalues during each periodic 1/320 second interval until the totalharmonic distortion satisfies a predetermined tolerance.

In the fourth part, the DC power is maximized, which results in themaximum power transfer. The apparatus can impedance match between thesource and the load. The controller modifies a power extractor parameter(e.g., a parameter 212, 222, of the apparatus) to maximize the extractedcurrent under then-current conditions, 326. Such power conversion can beperformed as described more below.

FIG. 4 is a block diagram of an embodiment of a system with multiplepower sources, a power extractor, and multiple AC loads. System 400represents a power transfer system having an inverter. As understood inthe art, an inverter is an electronic device or system that producesalternating current (AC) from direct current (DC). Generally the DC toAC conversion is accomplished as a conversion of square-wave DC currentto sinusoidal AC current. The inverter is generally the criticalcomponent in traditional photovoltaic (PV) and other renewable energysystems seeing it is responsible for the control of electricity flowbetween these energy systems and various electrical loads. The inverterperforms the conversion of the variable DC source to a clean 50-60 Hzsinusoidal alternating current (AC). Inverters also perform maximumpower point tracking (MPPT) ostensibly to keep power generation asefficient as possible. An inverter as described herein may also have acommunications interface to a central station for the transmission ofstatistics and alerts.

As illustrated, power extractor 422 may be a component of inverter 420.Thus, the inverter system may include a power extractor as the powertransfer element. System 400 includes one or more power sources 412-414,which can be dynamically coupled and decoupled to power extractor 422 toprovide DC current. In addition to power transfer, in system 400inversion circuitry 424 acts as a consumer of the output of powerextractor 422. One or multiple AC loads 442-444 may be selectively,dynamically coupled and decoupled to inverter 420 to receive power frominversion circuitry 424.

Inversion circuitry 424 generally converts the efficiently-transferredoutput power of power extractor 422 and converts and filters the powerin an efficient manner. The result is an inverter of much higherefficiency than systems implemented with traditional technologies.Discussions herein with regards to power distribution strategy,distributing power to one or more loads, or other power transferring,applies equally well to system 400 as it does to other describedembodiments. Similar issues of monitoring output power will be appliedin inversion circuitry 424 as are performed in power extractor 422. Themechanisms for monitoring the power output may be different in inversioncircuitry 424 than that of power extractor 422.

Inversion circuitry 424 is an algorithmically operated non-linearcurrent mode power converter. Inverter 420, via inversion circuitry 424,uses a geometric structure or topology to perform its current switchingfrom output provided by power extractor 422. The current switchingtopology technology converts DC power into AC power under microprocessorcontrol. The microprocessor may be a separate microprocessor than whatmay be employed in power extractor 422. The load requirements of ACloads 442-444 for voltage, frequency, and/or phase may be sensed undersoftware control and thereby implemented to a desired voltage,frequency, and/or phase. Alternatively, or additionally (for example, asan override), the load requirements for voltage, frequency, and/or phasemay be configuration controlled.

Load monitor 426 represents one or more components, whether hardware,software, or a combination (e.g., hardware with installed firmwarecontrol), which monitors the output of inversion circuitry 424 forvoltage (V), frequency (FRED), and/or phase. Based on what is detected,and/or based on rules or external input, load monitor 426 can provideconfiguration to inversion circuitry 424. Note that even when loadmonitor 426 is implemented in hardware, its input into inversioncircuitry 424 can be considered “software control” if input into amicroprocessor of inversion circuitry 424. Load monitor 426 may alsoinclude a communication connection (not shown) to, for example, acentral station that sends configuration parameters that are passed toinversion circuitry 424.

Additionally, or alternatively, to load monitor 426, inverter 420 mayinclude more “manual” configuration mechanisms. Such configurationmechanisms may include switches (for example, commonly usedconfiguration “DIP” (dual in-line package) switches. Other switches orcomparable mechanisms could also be used. DIP switches typically have arow of sliders or rockers (or even screw-type rotational mechanisms)that can be set to one or another position. Each switch position mayconfigure a different item, or the composite of all the switch positionscan provide a binary “number” input to a microprocessor. Frequencyselection 432 represents a configuration mechanism to set the outputfrequency of inverter 420. Voltage selection 434 can be used to selectthe output voltage of inverter 420. Phase selection 436 can be used toselect the output phase of inverter 420. The use of frequency selection432, voltage selection 434, and phase selection 436 can enable inverter420 to operate correctly even in cases where voltage, frequency, orphase information is provided incorrectly from a grid on which inverter420 operates.

FIG. 5 is a block diagram of an embodiment of a system that controlsharmonic distortion with a software feedback control subsystem coupledto a hardware waveform controller. System 500 includes power source 504,load 506, and output and control system 502. Power path 510 representsthe path of electrical power from source 504 to load 506, as controlledby output system 502.

Output system 502 includes input power converter 520 to receive inputpower from source 504 and convert it to another form (e.g., DC to AC).Input power converter 520 includes hardware components for receiving apower signal to convert, and may include appropriate power components.In one embodiment, input power converter 520 implements dynamicimpedance matching, which enables the input electronics to transfermaximum power from source 504. Dynamic impedance matching includesconstantly tracking a maximum power point, as well as driving an inputpower coupler (e.g., a transformer) to maintain as flat a power slope aspossible (e.g., slope of zero). Input power converter 520 may receivecontrol signals or information from controller 530, as well as providinginput to indicate operation of the converter.

Input feedforward 512 provides information (e.g., maximum power value,frequency as appropriate, or other information to control the inputpower converter hardware) about the source power to controller 530.Controller 530 controls input power converter 520 based on the inputinformation about the input power. Controller 530 represents any type ofprocessor controller that may be embedded in output system 502.Controller 530 may be or include any type of microcontroller, digitalsignal processor (DSP), logic array, or other control logic.Additionally, controller 530 may include appropriate memory or storagecomponents (e.g., random access memory, read only memory (ROM),registers, and/or Flash) to store code or values generated or obtainedduring runtime operation or pre-computed.

Controller 530 drives programmable waveform generator 540 to generatethe desired output waveform. Generator 540 also lies on power path 510,and receives input power from input power converter 520 to output. Whilethe power may be transferred, it is not necessarily output with the samewaveform as it is received. For example, a DC signal may be output as asinusoidal signal, as shown in the example of FIG. 5. Other powerconversions can be accomplished similarly as shown and described. In oneembodiment, generator 540 includes a PWM to generate output waveform508. Generator 540 receives control signals and information fromcontroller 530, and may provide status or operations information orfeedback to controller 530. The output waveform may be either current orvoltage.

Output system 502 is able to incorporate specific timing, phasing, orother frequency information, into generating output waveform 508. Suchtiming, phasing, or other frequency information may be referred to as“input synchronization data.” In one embodiment, such inputsynchronization data arrives from real-time load information, in whichcase it may be referred to as “load synchronization input.” The loadsynchronization input or input synchronization data indicatesinformation necessary to determine the synchronization signal discussedabove. Such information is indicated in output system 502 as output sync514. In a system where the output is anticipated (e.g., connecting to anelectrical grid), certain voltage, timing, or other information may beexpected (e.g., 520V at 60 Hz), and an initial estimate programmed in ormade by the system at startup. Based on load synchronization data, theinitial estimate may be adjusted.

Controller 530 also measures output feedback 516 off power path 510, todetermine the actual output generated by generator 540. The actualoutput is compared to an ideal reference to determine if the desiredoutput is being generated. In one embodiment, output feedback 516 is anabstraction to represent output measurement by controller 530, and doesnot include separate components in itself. In one embodiment, outputfeedback 516 includes a sampling mechanism or other data selectionmechanism to compare to the ideal reference signal. If output feedback516 includes components separate from controller 530, it may be drivenby controller 530, and receive comparison data from controller 530 andprovide error or feedback information. In one embodiment, outputfeedback 516 is understood to include at least hardware componentsnecessary for a feedback control process to interface with the outputlines. Additionally, output feedback 516 may include other hardware forperforming measurements, computations, and/or performing processing.

Both output sync 514 and output feedback 516 may be considered feedbackloops. It will be understood that output sync 514 and output feedback516 are not the same thing, and serve different purposes. Output sync514 indicates what the ideal reference signal should look like, asstored in reference waveform table 532. Output feedback 516 indicateshow the actual output varies from the reference signal. Update table 534represents data generated in response to output feedback 516. In oneembodiment, output sync 514 is based on voltage information on theoutput of power path 510, while output feedback 516 is based on outputcurrent generated at the output of power path 510.

Based on output sync 514 (or based on an initial estimate of the outputsync), output system 502 stores and/or generates reference waveformtable 532, which represents an ideal form of the output waveform desiredto be generated by generator 540. Reference waveform table 532 may bestored as a table or other set of points (or setpoints) that reflectwhat the output waveform “should” look like. While a sinusoidal waveformis represented, any periodic waveform could be used. Reference waveformtable 532 may alternatively be referred to as a reference waveformsource.

Based on output feedback 516, output system 502 generates update table534. Update table 534 includes entries or points to indicate how tomodify the operation of generator 540 to provide an output more closelymatching the waveform of reference waveform table 532. While indicatedas a table, update table 534 may be a stored table that is modified atcertain intervals (e.g., each entry is updated as necessary to reflectmeasured error data), or may be generated newly at each update interval.Update table 534 may alternatively be referred to as an update datasource. The “updates” may be modifications of old values, thereplacement of values, or may be stored in different locations within amemory accessed by controller 530. In one embodiment, each value ofupdate table 534 indicates an “up,” “down,” or no change for each of aset of points. Such values are applied to the hardware that controls theoutput of generator 540 to cause the output signal to converge on thedesired ideal waveform.

From one perspective, output system 502 can be viewed as having fivefeatures or components. While these features are depicted in FIG. 5 viacertain block diagrams, it will be understood that differentconfigurations and a variety of different components can be used toimplement one or more of these features. For purposes of discussion, andnot by way of limitation, these features are described following withreferences such as “Feature 1,” “Feature 2,” and so forth. It will beunderstood that such a convention is merely shorthand to refer to thesubject matter of the described feature or component, and does notnecessarily indicate anything with respect to order or significance.

Feature 1 may include means for incorporating specific timing, phasingor other frequency information. The means includes hardware and/orsoftware to generate and receive the input synchronization data or loadsynchronization input referred to above, which is based on output sync514. Feature 2 includes reference waveform table 532, which may includea table of data or an equation within software that represents the idealform of output waveform 508. Feature 3 includes controller 530, whichmay be or include a software algorithm that compares the actual outputwaveform generated by generator 540 with the ideal tabularrepresentation as represented by reference waveform table 532. Feature 4includes an algorithm within controller 530 that computes or otherwiseselects and generates update data represented by update table 534.Feature 5 includes generator 540 that uses the update data from updatetable 534 to generate output waveform 508 of the desired shape,proportion, timing, and phase.

With regard to Feature 1, the specific timing, phasing, or otherfrequency information provides synchronization information to thecomparison and update algorithms in controller 530. The information maycome by way of a table, equation, sampling of real-time hardwaremonitored signals, or other source.

With regard to Feature 2, the data representing the reference waveform,can be of any length and of any format, integer or non-integer, ifwithin a table. Such a table may be generated dynamically at runtime orbe hard-coded at compile time. The ideal form of the waveformrepresented may be sinusoidal or non-sinusoidal. The waveform may berepresented by data values evenly spaced in the time domain ornon-evenly spaced, forward in time or backward in time or any mixthereof. The waveform could alternatively be represented by data valuesin the frequency domain, and organized in any fashion. The data may becompressed or non-compressed. The data may be represented by an equationrather than computed data setpoints, or part by an equation and part bya table. In one embodiment, the stored setpoints in a table are thecomputed results of an equation. The data may be altered duringprocessing at runtime to change the form of the ideal waveform to adifferent ideal. The values in reference waveform table 532 can bemodified or replaced with different values if altered at runtime. Thedata may be aligned to be in exact phase with the input waveform or itmay be shifted in phase.

With regard to Feature 3, controller 530 may include any traditional orstandard comparison algorithm. A control algorithm compares data valuesrepresenting the output waveform, sampled by hardware, and transformedinto software data values through standard or non-standard samplingtechniques. In one embodiment, the controller compares the idealsetpoints of the table or equation computations with the synchronizationinformation, point by point, and generates error data, point by point.In one embodiment, the controller can process multiple points at onceinstead of point-by-point.

With regard to Feature 4, controller 530 includes a selection algorithmwhich creates or generates new data using any standard or non-standardtechnique. In one embodiment, the selection algorithm involvesperforming calculations. Alternatively, the selection algorithm maysimply select data without performing processing or performingcalculations. The selection algorithm may replace data values in a tableof setpoints, or leave the data values in the table preferring to useanother storage area. The selection algorithm may transform the datafrom the time domain to the frequency domain and vice-versa as part ofits selection process. The algorithm provides an error update mechanism(e.g., algorithm) in that it identifies data values that will correctthe output waveform when applied. Thus, the output waveform afterapplication of the data values appears more like the preferred idealwaveform.

With regard to Feature 5, the new data values represented by updatetable 534 are applied to hardware in generator 540 through standardprocesses to drive the generation of the output waveform. In oneembodiment, the new data values are applied via a PWM mechanism or anyother mechanism that transforms discrete data values into an analogoutput form.

FIG. 6 is a block diagram of an embodiment of a system that controlsharmonic distortion. In one embodiment, system 600 of FIG. 6 is anexample of a grid-tied power conversion system implementing system 500of FIG. 5. Thus, input 602 may correspond to input power from source502, and output 650 may correspond to an output at load 506. In oneembodiment, system 600 controls harmonic distortion of the outputcurrent signal and the phase shift between the grid voltage and theoutput current signal of a grid-tied solar photovoltaic or other source,DC to AC power conversion system.

System 600 inverts input DC power 602 into output AC power at output650. In one embodiment, the voltage and current at output 650 are bothideal 60 Hz sinusoidal waves, undistorted by spurious harmonics, wherethe current either lags or leads the voltage by a phase shift. Such animplementation can be employed in a grid-tied system, where the outputvoltage is firmly established by the grid-tie at output 650, but thecurrent is not. Regulations UL 1247 require that the current be reducedin harmonic distortion. As illustrated, system 600 provides at least theformation of an ideal sinusoidal waveform, shifted in phase from thefixed voltage of the grid, yet undistorted in aspect.

In one embodiment, the operations of system 600 can be separated asthree elements. The first is to establish a table of ideal currentwaveform values for the desired waveform with a desired angle of phaseshift without distortion. While described more specifically to outputcurrent waveforms and ideal current waveforms, it will be understoodthat such is a non-limiting example, and the discussion with respect tosystem 600 could be applied also to controlling output voltagewaveforms, with modifications that will be understood by those skilledin the art. The second is to compare an actual output signal generatedby a waveform generator to the ideal waveform. The third is to generate,with input timing information and the error information, an update tableof values that allows the waveform generator to correct the actualoutput waveform. The operations iteratively improve the output waveformtending toward the ideal waveform (e.g., a sinusoid). Thus, the resultof the operations places a pure 60 Hz current waveform in-phase with,leading, or lagging the grid voltage waveform.

The main power flow-through path in one embodiment occurs as follows:Input 602 is DC input power. PWM generator 630 drives DC-to-AC converter642 using a table of updated values (PWM table entry update 680). In oneembodiment, update table 680 corresponds with table 540 of FIG. 5. InputDC power 602 passes into DC-to-AC converter 642 of inverter hardware640, and leaves as output AC current waveform 650. Current waveformdetector 644 detects the current waveform at output 650. The inputwaveform is illustrated at PWM generator 630 as a perfect sine wave, anddistorted at current waveform detector 644. The amount of distortion maybe exaggerated, but illustrates that the output waveform may not eveninitially look much like the ideal desired waveform. However, thewaveform converges through the feedback. Inverter hardware 640 alsoincludes voltage waveform detector 646, which generates sync information648, which corresponds to the output sync information of FIG. 5.

The control loop flow detecting and implementing the feedback occurs asfollows: Information about the DC input power 604 and input phase shiftinformation 606 refines a reference ideal waveform 610. The referenceideal waveform, as discussed above, can be stored as a table. In oneembodiment, simultaneously the output of PWM generator 630 is peakdetected 622 and allowed to scale the ideal table in reference waveformlevel control 624. The output of level control 624 is the instantaneousideal waveform desired. The reference waveform from reference waveformlevel control 624 and the actual output is received at PID(proportional-integral-derivative) controller 660.

PID controller 660 includes PWM table error detector 662, which receivesthe scaled reference waveform and the actual output waveform. The errorbecomes the error input for proportional error block 664, integral errorblock 666, and derivative error block 668. The sum of the error signalsis PWM table error sum, which provides the PID controller output to PWMtable entry update 680. These updated table values are fed back into PWMgenerator 630 and drive the generator to adjust the output of inverterhardware 640, to converge the output signal to reference waveform 610.

FIG. 7 is a block diagram of an embodiment of a system with multiplepower sources, a power extractor, and multiple loads. System 700provides a general use case scenario for power extractor 730. Powerextractor 730 is an example of a power extractor according to anyembodiment described herein. There may be one or more power sources712-714 coupled to power extractor 730. Note that different powersources may require different coupling hardware. Input coupling hardware720 includes interface circuits that couple the input power sources topower extractor 730. In some embodiments, interface circuit 722 isdifferent from interface circuit 724. However, they may be the same.

Power sources 712-714 may be any type of DC power source (referred to asa power source or an energy source). In general, examples of DC powersources that may be used in accordance with embodiments of a powerextractor include, but are not limited to, photovoltaic cells or panels,a battery or batteries, and sources that derive power through wind,water (e.g., hydro-electric), tidal forces, heat (e.g., thermal couple),hydrogen power generation, gas power generation, radioactive, mechanicaldeformation, piezo-electric, and motion (e.g., human motion such aswalking, running, or other motion). More specifically with respect tothe grid-tied systems discussed herein, power sources 712-714 includeany power source capable of providing power to a grid-tied load.

In general, power sources may include natural energy sources andman-made power sources, and may be stable (providing an essentiallyconstant power but variable in magnitude) and unstable (providing powerthat varies over time). Input coupling hardware 720 may be considered toinclude the entire interface (e.g., from the cable/wire/trace to theconnector/pin to the circuitry), or simply include the interfacecircuitry. The interface circuitry may include any type of discretecomponents (e.g., resistors, capacitors, inductors/transformers, diodes,or other electronics components) as is described herein, and as mayotherwise be known in the art.

Additionally, in some embodiments, input coupling hardware 720 includesswitches (e.g., power field effect transistors (FETs)) or other similarmechanisms that enable one or more power sources to be selectivelydisconnected or decoupled from power extractor 730. The coupling anddecoupling of power sources can be performed, for example, via controlsignals from a management portion of the power extractor.

Similar to the input side, either power extractor 730 includes, or elsethere is coupled to power extractor 730 in system 700, output couplinghardware 740. Output coupling hardware 740 includes interface elements742-744. There may be a one-to-one relationship between interfaceelements 742-744 and loads 752-754, but such a relationship is notstrictly necessary. One or more loads can be coupled via the same outputcoupling hardware. A similar configuration can exist in input couplinghardware 720—the relationship of elements to sources may be one-to-one,or some other ratio. With a ratio other than one-to-one, there may berestrictions on selectively bringing individual sources or loads on- andoff-line. Such restrictions could result in reduced efficiency (from anideal otherwise potentially achievable) in impedance matching, thoughgroup matching may not necessarily be less efficient. Thus, loads and/orsources may be handled as groups, which can then be brought online oroffline as a group, and impedance matched as a group.

Loads 752-754 may also be selectively coupled to power extractor 730 viaoutput coupling hardware 740. One or more loads may be coupled ordecoupled via a control signal in accordance with a management strategy.Power transfer manager 734 generally represents any type of powertransfer management circuit, and may include one or more processingcircuitry elements, such as microprocessors, field programmable gatearrays (FPGA), application specific integrated circuits (ASIC),programmable logic arrays (PLAs), microcontrollers, or other hardwarecontrol logic. Management of the power transfer is performed by powertransfer manager 734, which can be considered to operate according to apower transfer management strategy. Such a strategy controls how powerwill be transferred, or how power transfer manager 734 will operate tomanage power transfer. Operation to manage power transfer may includesetting output lines to an active or inactive state (e.g., toggling amicroprocessor I/O pin), or otherwise sending configuration controls toother circuits.

Power transfer manager 734 monitors the input power for power changes todetermine how to control the operation of power transfer circuitry 732.Power transfer circuitry 732 is described in more detail below, andgenerally enables power extractor 730 to convert power from the sourcesinto power to deliver to the loads. It will be understood that with theability to selectively couple and decouple sources and loads, powertransfer manager 734 may include logic to adjust the power transferaccording to any of a number of power transfer scenarios. Such abilityenables dynamic system configuration changes while power extractor 730maintains transfer efficiency.

Power transfer manager 734 and power extractor 730 can dynamically andcontinuously adjust to system configurations, as well as continuouslymonitoring input and/or output power curves. The logic accounts for theneeds of the load(s), and the input of the source(s). In someembodiments, the needs of the loads can be determined by monitoringhardware. A simpler method is to include power profiles of the intendedloads, which informs power transfer manager 734 how to control theoutput for particular loads. Power transfer manager 734 can identifywhich loads are present, and thus which profiles are applicable, basedon load detection/monitoring, and/or via indication of a load by anexternal source (e.g., the load itself sends a signal such a triggeringa load pin on a microprocessor, or a system management entity indicateswhich loads are present).

One inefficiency of traditional systems is the “always on” aspect to theswitching supplies. Traditional power transfer technology consumed powereven when the loads did not require power, and/or even when a source wasnot available. Thus, some part of the power transfer circuitry wasalways consuming power. In some embodiments, power transfer manager 734can automatically turn power extractor 730 on and off based on thepresence of power and/or load. Thus, for example, power transfer manager734 may automatically enter a sleep state if the input power drops belowa threshold (e.g., 1.0 mA at 5V). When the power is above the threshold,power transfer manager 734 may determine whether any loads are or shouldbe connected. In the absence of source and/or load, power transfermanager 734 may not provide control signals, which results in no powertransfer, or may produce signals to deactivate active circuitry. Powertransfer manager 734 can be sophisticated and also or alternativelyinclude a timer mechanism that enables the system to wake up after aperiod of time (e.g., 5 minutes) to re-check on the status of thesystem.

In some embodiments, the concepts of power management as embodied bypower transfer manager 734 may be considered to include multipleaspects. For example, power management may include business rules andcontrol, where each rule may control a different aspect of powercontrol, or control the same power control aspect in a different manner.Business rules and control may be implemented as hardware, software, orsome combination. The business rules may be broken down into planningrules, which are strategic rules that may look at impedance matching ormonitor the power curve. Organizational rules may be tactical rules thatdetermine how to deal with the multiple inputs and multiple outputs. Therules may provide and/or implement parameters that provide theparticular functionality of power extractor 730. The control canimplement actions or put into effect the business rules. For example, insome embodiments, impedance matching may match only a single powersource. Selective matching would be performed for the input source thatmakes the most sense to match.

In some embodiments, determining how to transfer power to the loads ordetermining a power transfer strategy includes determining oridentifying and selecting power distribution rules. The power transferthen occurs in accordance with the selected power distribution rule.Power distribution rules can be simple or complex, and may be generallyclassified as follows.

Hierarchical rules result in a simple precedence of one load overanother. As source power fluctuates up and down, the power transferredto the loads may be to give preferential treatment to one load over theother. An example may be to favor the operational circuitry of amission-critical device, while giving lower preference to a rechargingone of several backup batteries.

Round robin rules institute a schedule for distributing power. Forexample, power can be distributed to one load for a period of time, thento another, then to another. Thus, all loads would receive some portionof distributed power in a given period of time. Allocation-based rulesmay institute fixed allocations for each load. For example, a system mayallocate 80% of all distributed power to charging a main battery,leaving 20% for one or more other loads.

Time based rules allow the distribution of power to be based on the timeof day, or time of week. For example, a system can be programmed with asunrise/sunset schedule and have logic to determine peak sun hours.Thus, power may be expected to be at a peak from a solar panel atparticular times of day. Based on the time of day, the system maydistribute power according to one strategy or another. In anotherscenario, a system may have historical data that indicates peak loaduse. Power may be distributed at certain times of day according to theexpected use. Note that as described below, peak input power and peakload may be actively determined and dynamically accounted for. Timebased rules may then act as a framework for other rules to be applied.For example, during certain times of day, a round robin may be used,while a demand based strategy is employed at other times of day.

Functionality based rules enable the system to allocate power accordingto the load's functionality or purpose in the system. For example, in apacemaker, the functional circuitry can be given priority over batterycharging. Similarly, navigational equipment may be given a preferentialtreatment over cabin lights in an aircraft. Demand based rules canadjust the power transfer to be commensurate to demand of the loads.Demand based rules may require the addition of detection circuitry (notshown) in output coupling hardware 740. In some embodiments, powerextractor 730 includes load balancing logic (hardware and/or software)to implement demand based rules. In some embodiments, command basedrules can also be applied. That is, a central station or other controlentity can provide a rule for how power should be distributed, which mayoverride any other rules or conditions already in the system.

As already suggested, the power distribution rules can be appliedconsistently, or may be adjusted for any of a number of scenarios (e.g.,change in demand, time of day, number/strength of power sources, orother variable condition).

Power transfer manager 734 may include or have associated impedancecontrol 736. Impedance control 736 may refer to hardware and softwarethat matches the impedance of input coupling hardware 720 and/or outputcoupling hardware 740 with associated sources or loads, respectively.Techniques for impedance matching are described above, and will not berepeated here.

FIG. 8 is a block diagram of an embodiment of a power extractor. Powerchange analysis circuitry 820 includes power change detection circuitry830. Power transfer circuitry 870 includes circuits 872, 874, and 876.Circuits 872 and 876 include transformer T1 (including inductors L1 andL3) and transformer T2 (including inductors L2 and L4). Circuit 874includes capacitors C1 and C2 and node N5 separating C1 and C2, andconnected to inductors L3 and L4. Power source 802 is coupled toinductor L1 through conductor 804 of node N1, an interface connector,and a node N1*. The (*) designates the effective node, or the equivalentnode seen looking into the system from the outside (N1* is seen fromsource 802, and N2* is seen from load 890). As an example, the interfaceconnector may be a plug receptacle. If the impedance difference betweenN1, the interface connector, and N1* are relatively small, then they maybe considered one node. Otherwise, they may be considered more than onemode. Likewise with node N2*, a corresponding interface connector, andnode N2. Inductor L1 is between nodes N1* and N3, and inductor L2 isbetween nodes N4 and N2*.

Power change detection circuitry 830 detects a power change of power atnode N1* and provides a switching control signal on conductor 838 (fromelement 836) to one input of comparison circuit 840. In one embodiment,power change detection circuitry 830 detects a slope of the power changeand may be called power slope detection circuitry 830, and provide apower slope indication signal. In one embodiment, the power slope is aninstantaneous power slope. Another input of comparison circuit 840receives a waveform such as a saw tooth wave from waveform generatorcircuit 826. Comparison circuit 840 controls a duty cycle of switches S1and S2. In one embodiment, S1 and S2 are not both open or both closed atthe same time (with the possible exception of brief transitions whenthey are switching). Waveform generator circuit 826 and comparisoncircuit 840 are examples of circuitry in switching control circuitry880.

When S1 is closed, electromagnetic fields change in T1 and T2 while theelectrostatic potential across C1 and C2 is altered and energy frompower source 802 is distributed electromagnetically into T1 and T2,while electrostatically in C1 and C2. When S1 opens, S2 closes and themagnetic flux in T1 begins to decrease. Thus, the energy stored in T1flows through N3 to capacitors C1 and C2 of circuit 874, depositing someof the energy as an electrostatic field onto C1 and C2, and some of theenergy into T2 of circuit 876 through node N5 and inductor L4. Theresidual flux in T2 also begins to decrease, transferring energy intoload 890 through N2. When S1 closes and S2 opens again, the magneticflux in T1 begins to increase while the magnetic flux T2 also increasesas it consumes some of the electrostatic energy that was previouslystored onto C1 and C2. Thus energy stored in circuit 874 is dischargedand transferred to T2 and the load. By driving the switches at a properfrequency, T1 and T2 can be driven to saturation, resulting in anefficient transfer of energy from source 802 to the load.

Multi-phase energy transfer combines two or more phased inputs toproduce a resultant flux in a magnetic core equivalent to the angularbisector of the inputs. (Note: an angle bisector of an angle is known tobe the locus of points equidistant from the two rays (half-lines)forming the angle.) In this embodiment of the power extractor,capacitors C1 and C2 are used to shift the phase of the current that isapplied to the secondary winding of T1 and T2 (L3 and L4 respectively).Thus, multi-phased inputs are applied to the cores of T2 and T3. Thesummation of the multiphase inputs alter the electromotive force thatpresent during the increase and reduction of flux in the transformer'sprimary windings L1 and L3. The result is the neutralization (within thebandwidth of the operational frequency of the power extractor) of highfrequency variations in the reactive component of the impedance thatcircuits 872 and 876 exhibit to the source and load respectively.Circuits 872 and 876 may be multiphase bisector energy transfer circuitsto cause the multiphase bisector energy transfer and to interface withcircuit 874.

Due to the dynamic properties of circuit 872, power source 102 “sees” anequivalent impedance at inductor L1 of power extractor 810. Likewise,with inductor L2 and load 890. The input and output impedances of powerextractor 810 are adjusted by controlling the duty cycle of S1 and S2.Optimal matching of impedances to the power source 802 occurs whenmaximum power extraction from the power source is achieved.

Power slope detection circuitry 830, power change indication signal, andcomparison circuitry 840 are part of a control loop that controls theduty cycle of switching circuitry 850 to achieve maximum powerextraction (i.e., ΔP/ΔV=0) from power source 802. The control loop mayalso control the switching frequency of switching circuitry 850 toinfluence the efficiency of power transfer through the power transfercircuitry 870. Merely as an example, the frequency may be in the rangeof 100 KHz to 250 KHz depending on saturation limits of inductors.However, in other embodiments, the frequencies may be substantiallydifferent. The size and other aspects of the inductors and associatedcores and other components such as capacitors can be chosen to meetvarious criterion including a desired power transfer ability,efficiency, and available space. In some embodiments, the frequency canbe changed by changing the frequency of the waveform from waveformgenerator circuit 826. In some embodiments, the frequency is controlledby a control loop as a function of whether an on-time rise of current isbetween a minimum and maximum current in an energy transfer circuit.

As used herein, the duty cycle of switching circuitry 850 is the ratioof the on-time of S1 to the total on-time of S1 and S2 (i.e., dutycycle=S1/(S1+S2)). The duty cycle could be defined by a different ratioassociated with S1 and/or S2 in other embodiments. When the voltages ofpower source 802 and load 890 are equal and the duty cycle is 50%, thereis zero power transfer through power extractor 810 in some embodiments.If the voltages of power source 802 and load 890 are different, a higheror lower duty cycle may cause zero power transfer through powerextractor 810. Thus, a particular duty cycle of switching circuitry 850is not tied to a particular direction or amount of power transferthrough power transfer circuitry 870.

It will be understood that the power change can be continuously detectedand the switching control signal can be continuously updated. Usinganalog circuits is one way to perform continuous detection and updating.Using digital circuits (such as a processor) is another way to performcontinuous detection and switching control signal updating. Even thoughthe updating from some digital circuits may in some sense not be exactlycontinuous, it may be considered continuous when for all practicalpurposes it produces the same result as truly continuous updating. As anexample, the updating of the switching control signal is also consideredcontinuous when the frequency of change is outside the control loopbandwidth. In some cases, the updating of the switching control signalalso could be considered continuous when the frequency of change iswithin the control bandwidth. Merely as an example, in someimplementations, the control loop bandwidth may be around 800 Hz. Inother embodiments, the control loop bandwidth is higher than 800 Hz, andperhaps much higher than 800 Hz. In still other embodiments, the controlloop bandwidth is lower than 800 Hz and depending on the desiredimplementation and performance may be lower than 400 Hz.

A processor/ASIC and/or field programmable gate array (FPGA) 822(hereinafter processor 822), scaling circuitry 824, current sensors (CS)862 and 864 may also be included. Processor 822 receives signalsindicative of the sensed current as well as voltage of node N1*. LettersA and B show connections between the current sensors and processor 822.In one embodiment, processor 822 also gathers information and/orprovides control to sub-loads. The current information can be used toindicate such information as the rate, amount, and efficiency of powertransfer. One reason to gather such information is for processor 822 todetermine whether to be in the protection mode (such as the second mode)or the ordinary operating mode (such as the first mode).

In a protection mode, there are various things processor 822 can do toprovide protection to power extractor 810 or load 890. One option is toopen both switches S1 and S2. Another option is to provide a bias signalto scaling circuitry 824, which is combined in circuitry 836 with apower slope indication signal to create the switching control signal onconductor 838. For example, if the bias signal causes the switchingcontrol signal to be very high, the duty cycle would be low causing thecurrent to be small. The regulation of power in the protection mode canbe to completely shut off the power or merely to reduce the power. Inthe protection mode, the goal is no longer to maximize the powertransferred. In some embodiments, the bias signal is asserted forpurposes other than merely protection mode.

Additionally, current sensors 852 and 854 provide signals indicative ofthe current through switches S1 and S2, which are summed in summer 856.Power may be related to the average current from summer 856. These maybe provided to integrator 858 to provide a signal indicative of thepower, which is differentiated by differentiator 832 and amplified byamplifier 834.

FIGS. 9-13 each illustrate a block diagram of an embodiment of powertransfer circuitry. The power transfer circuitry of FIG. 8 is reproducedin FIG. 9, and can be compared with alternative power transfer circuitryillustrated in FIGS. 10-13. The values of the resistors, capacitors andinductors (such as R1, R2, C1, C2, C3, C4, L1, L2, L3, L4, L5, and L6)are not necessarily the same in each figure. Reference below tomodifications of circuits 872, 874, and 876 will be understood to bemodifications with reference to what is depicted in FIG. 9.

Referring to FIG. 10, circuits 872 and 876 are modified to include an RCcircuit between inductors L3 and L4 and ground. Thus, the node of L3connected to ground in FIG. 9 connects to R1 and C3 in parallel, whichin turn connect to ground. Similarly, L4 connects to R2 and C4 inparallel, which in turn connect to ground. Additionally, circuit 874 ismodified to include L5 connected between L3 and L4. N5, rather thanbeing connected to L3 and L4, is connected (most logically in themiddle) to the windings of L5.

Referring to FIG. 11, circuit 872 is modified to include resistor R1between L3 and ground, and circuit 876 is modified to include resistorR2 between L4 and ground. Additionally, circuit 874 is modified toinclude inductor L5 between L3 and node N5 and inductor L6 between L4and node N5. Capacitor C3 is connected between L3 and L4.

Referring to FIG. 12, circuit 872 is modified to include inductor L5connected to L3, and L5 in turn connected to the parallel RC circuit ofR1 and C3 to ground. Similarly, circuit 876 is modified to includeinductor L6 connected to L4, where L6 is connected R2 and C4 in parallelto ground.

Referring to FIG. 13, circuit 872 is modified to include inductor L5between L3 and ground, and circuit 876 is modified to include inductorL6 between L4 and ground. Circuit 874 is modified to connect R1 betweenL3 and N5, while R2 is connected between L4 and N5. Additionally,capacitor C3 is connected between L3 and R1 and ground. Similarly,capacitor C4 is connected between L4 and R2 and ground.

FIG. 14 is a block diagram of an embodiment of cogeneration of powerfrom a local source and a utility grid to a grid load that neighbors thelocal source. System 1400 transfers power from a local source to agrid-tied load with power factor conditioning. System 1400 represents apower system that includes metastable source 1410, inverter 1420, loadZ1402, and utility power grid 1430. Load Z1402 represents a firstconsumer premises tied to grid 1430, and load Z1404 represents a secondconsumer premises tied to grid 1430. Load Z1404 is not within the sameelectrical system with respect to a connection point to grid 130 as loadZ1402, and is thus not local to load Z1402.

However, load Z1404 may be a neighbor, in that power output generatedfrom a power source local to load Z1402 may be directed to load Z1404with measurable effect. A load is not a neighbor for electrical purposesof the power sources if the load is far enough away geographically thatthe effect of power transfer from load Z1402 to Z1404 is only negligiblygreater than an effect to the grid as a whole.

Source 1410 and inverter 1420 are local to load Z1402, and provide powerto the load. In one embodiment, under normal operation, DC power isdrawn from source 1410, and extracted, inverted, and dynamically treatedby inverter 1420, to dynamically produce maximum AC current relativelyfree of harmonic distortion and variability, and completely in phasewith the AC voltage signal from power grid 1430. Putting the generatedAC current in phase with the grid AC voltage produces AC power with apower factor at or near unity to load Z1402, meaning that all reactivepower drawn by the load comes from grid 1430. If source 1410 producesmore energy than is needed to satisfy the real power requirements ofload Z1402, the power-corrected and distortion-filtered power may bedelivered to grid 1430 for further distribution.

The threshold voltage for transferring power to grid 1430 may be 3-5%above the average voltage of the grid. Ideally, the customer associatedwith load Z1402 would be compensated for the value of the excess powerprovided to grid 1430, either in the form of cash payments or asdeductions from the cost of power consumed from grid 1430.

Excess power from source 1410 that is fed back to grid 1430 may betransferred to satisfy the load requirements of a neighbor load (e.g.,load Z1404 of a second grid customer). In various embodiments, power maybe transferred beyond a single transformer. In addition to providingtraditional cogeneration power to grid 1430 (the power having desirablepower factor and distortion characteristics), the operation of system1400 can be modified to provide power having other characteristics thatmay be more desirable to grid 1430 (e.g., the utility company),particularly at times of peak power consumption.

More particularly, inverter 1420 may be configured (statically ordynamically) to produce power with current and voltage leading orlagging the other. In this way, power may be produced with a powertriangle exhibiting inductive or capacitive reactive power that may beused by the utility to counteract or offset accretions of capacitive orinductive power, respectively, within a region of load Z1402. Again, thepotential effect created by a single inverter 1420 on the grid may nottransfer beyond one or two hops along the power grid. However, one ormultiple inverters in a region can be effective at providing control intheir local region, among a group of neighbors, for example. When thateffect is multiplied by having such inverters in many neighborhoods, thegrid can much more effectively be managed by local as well as utilitypower grid control.

FIG. 15 is a block diagram of an embodiment of a power factor enhancedpower supply. In various embodiments, the efficiency of a power supplycan be increased based on power factor enhancements. AC/DC powersupplies have efficiency measured by comparing the AC power delivered tothe supply with the DC power delivered to the load. With power factorconditioning as illustrated in system 1500, higher efficiency powersupplies can be provided based on principles of power factor control asdescribed herein.

System 1500 includes grid AC 1510, which is an AC power source. Ratherthan sending AC input directly to AC/DC converter 1524 as would be donein traditional systems, power factor (PF) enhanced power supply 1520(hereinafter “power supply 1520”) first conditions the power factor ofthe incoming AC power. Power factor conditioner 1522 modifies the inputAC signal from source 1510 to deliver power to power supply 1520 havinga power factor at or near unity at the input. At or near unity, orputting one signal in phase with another can be understood to mean thatpower factor is within a tolerance of a few percentage points fromunity. It will be understood that power factor may not immediately reachunity, but there may be an adjustment period of up to several seconds toallow the system to condition the power factor to the desired value.

By creating a unity or near unity power factor at the input of the powersupply, more real power is delivered to power supply 1520, which in turnincreases the efficiency of DC power delivery to DC load 1530. Thus, theefficiency of the combined power factor conditioner and power supplywith respect to the power provided by source 1510 is greater than thatof a traditional power supply alone.

FIGS. 16A-B illustrate an embodiment of phase, active, and reactivepower that are controlled by power factor conditioning. As is understoodin the art, the term “reactive power” refers to the power associatedwith voltage and current out-of-phase by 90 degrees. Power in which theangle is out-of-phase by some other amount, for example, 80 degrees or30 degrees, is a “mixture” of both active and reactive power.

Consider a right triangle as illustrated in FIG. 16A. In the triangle,base 1606 represents a voltage waveform, and hypotenuse 1604 representscurrent waveform. The angle 1602 between the voltage and currentwaveforms is the same angle as between active and apparent power.Adjusting the angle between the current waveform and the voltagewaveform conditions the power factor to or toward a desired value.

FIG. 16B illustrates the right triangle with base 1614 representing theamount of active power, and vertical side 1616 representing the reactivepower. Thus, angle 1602 between the horizontal or base and thehypotenuse (apparent power 1612) is the same as the angle between thevoltage and current that together generates these powers. It will beunderstood that the length of hypotenuse 1612 is constant, and hencerides the circumference of circle 1610. Hypotenuse 1612 represents the“apparent” power. As angle 1602 increases, active power 1614 decreases,while reactive power 1616 increases. It is therefore possible, bycontrolling the phase angle to control the mix of active and reactivepower.

The term “power factor” refers to the ratio of active 1614 to apparent1612 power. It will be understood that the apparent power remainsconstant; thus, as angle 1602 increases, the power factor decreases.Therefore, an exactly meaningful, but considerably shorter, term for“phase angle between voltage and current” is “power factor”. In thetechnical language, the two terms are used interchangeably. The maximumpower factor equals 1, when phase angle 1602 has a value of 0. Theminimum power factor equals 0, when phase angle 1602 is 90 degrees.

With the advent of adaptive generation and control of arbitrarywaveforms at the electrical grid-tie by the power factor can be managedand controlled at the output of the inverter. Controlling the powerfactor at the output of the inverter is beneficial to the utilitiesbecause it provides an alternative means of providing the localdistribution system with reactive power. The utilities therefore saveconsiderable sums when local sources (e.g., solar photovoltaic (PV)systems) supply this reactive power, than if they have to produce itthemselves or compensate for it locally.

The State of California, United States, recently required utilitiesoperating in that state to pay solar PV owners for both active andreactive power when these owners supply them to the grid. It is expectedthat other states will follow suit. Therefore, there is considerablebenefit to PV owners to supply a mix of both types of power depending ontheir agreed tariff and/or PPA.

The utilities therefore have an incentive to produce tariffs encouragingPV owners to construct power factor controlling PV systems, while PVowners have the incentive to use them on their PV systems. Supplyingpower to the grid from a PV (or other local source) system based on gridconditions (e.g., time of day, reactive and/or active power needs) cancreate a benefit to both the utility and the consumers.

FIG. 17 is a block diagram of an embodiment of a system that controlspower factor at a local load. System 1700 shows a typical inverter 1720(e.g., a solar PV inverter), which controls the power factor at point“A”, tied to utility electrical grid 1740 (hereinafter “grid 1740”)through electrical measuring meter 1730 (hereinafter “meter 1730”).Point B represents the point of connection to grid 1740 for local loadZ1702 and the electrical system associated with it (i.e., includingsource 1710 and inverter 1720). By providing a proper mix of active andreactive power, the benefits to owner of source 1710 are maximized,according to agreed-on elements of a tariff at meter 1730. Such controland management can occur either on demand, as, for example, by remotecontrol communications to remote control algorithms 1728, or byautomatic software algorithms 1726, both built into inverter 1720itself. Inverter 1720 also includes inversion processor 1722 to providepower transfer functions as described above. Inversion controller 1724controls the operation of inversion processor 1722 to convert power andcondition the power factor.

It is possible to control the power factor at either Point B or Point Cby controlling the power factor at Point A. It will be understood thatPoint C can be interpreted as anywhere on the grid. There are practicallimits in distance to trying to control power factor too far away frommeter 1730. Thus, Point C may be just beyond the meter, or somereasonable distance beyond the meter. There is an implementation inwhich monitoring can be done by the utility (for example, by using WiFi(e.g., 802.1x wireless systems)) for all or many of the arrays in aneighborhood or geographic area. Assuming there is a neighborhood of PVarrays automatically correcting for power factor, they can coordinate tobenefit the utility if the utility has tariff agreements with theneighborhood owners to control their output power factor. In such animplementation, those inverters might need to know the power factorbeyond the meter, but not so far away that it becomes meaningless.

FIG. 18 is a block diagram of an embodiment of a system that controlspower factor on a grid-facing connection by controlling power factor ata local load. System 1800 illustrates controlling the power factor ateither Point B or Point C by controlling power factor at Point A. At anymoment in time, the amount of power flowing into local load Z1802 isdictated by the characteristics only of the load, and not by anythingelse. That power can come from either inverter 1810 (from a localsource), from grid 1830, or from both together. Both inverter 1810 andgrid 1830 produce an apparent power, which consists of both active andreactive power (refer to FIGS. 16A and 16B above).

Hence, if an established tariff has the customer of Z1802 paying onlyfor active power supplied by grid 1830, the best benefit to the consumeris to reduce the flow of active power from the grid across meter 1820.In that case, inverter 1810 should supply all active power and noreactive power, to satisfy the demands of local load Z1802. The reactivepower needed by load Z1802 is then supplied in total by the grid.Reducing the phase angle at Point A will of necessity cause all reactivepower to come from the grid. It will be understood that if the powerfactor of power from inverter 1810 is unity (1), then the reactive powercomponent coming from inverter 1810 is zero, and all reactive power mustbe supplied by grid 1830. Thus, controlling the power delivery at pointA necessarily affects the power coming into the electrical system frompoint B.

On the other hand, if an established tariff requires the customer to paya higher cost for the reactive power than for the active power, the bestbenefit is for the inverter to provide all of the demands of load Z1802for reactive power, while letting the grid supply most, if not all, ofthe load's active power demand. Increasing the phase angle at Point Awill accomplish that goal for similar reasons to those mentioned above.

It may be that the best benefit to a customer according to anestablished tariff is to produce a mix of both active and reactivepower. To the extent both can be supplied from a local power source, theneeds of the local load can be satisfied by the local source. To theextent the local source supplies more than the local load requires, theremainder of the generated conditioned power can flow out onto grid1830.

Thus, it will be understood that “best benefit” to the customer dependsupon what an established tariff dictates. In many cases the best benefitcan be calculated dynamically and applied in real time. For example,software algorithms embedded in the controlling apparatus of inverter1810 can perform the calculations. At other times and situations, “bestbenefit” settings can be applied remotely through communications links.

FIG. 19 is a block diagram of an embodiment of a system that controlspower factor at a grid connection by controlling power factor at a powersource farm. In the case of a large local power source, such as a verylarge PV array, or a green energy “farm” (such as a “solar farm”), the“best benefit” at some particular moment may be controlled by the needsof the utility instead of the needs of the consumer. For example, theutility may be in need of an insertion of reactive power to the grid tosupport drooping voltages. In such a case, the utility may have deviseda tariff, attached to a PPA (power purchase agreement), which gives theutility the right to control the power factor settings at the output ofthe solar farm. The power factor settings can be controlled remotely bythe utility, rather than by local decision-making.

System 1900 illustrates such a scenario of a power source “farm”controlled by a master controller. System 1900 includes multipleinverters 1912-1916. Each inverter has an associated remote controlmechanism 1922-1926, respectively. The remote control mechanisms mayinclude communication interfaces (including connectors, physicalnetworking interfaces, protocol stacks, and anything else necessary tocommunicate and receive commands remotely). The remote controlmechanisms then also have control logic to apply the remotely receivedcommands to adjust performance or output of the associated inverter.

The operation of the inverter is described above with respect to otherfigures. In addition to applying changes in response to a feedbacksignal, or instead of applying changes in response to a feedback signal,an inverter can apply changes in response to a remote command. Thecommand may indicate a desired power factor, a delta or correctionvalue, a relative value that can be applied, or may indicate to measurelocally and correct based on measured values.

Master controller 1932 may be located at a utility, or may be a mastercontroller located within the same electrical system as the inverters(i.e., on the same side of the point of connection to grid 1950). Mastercontroller 1932 includes software algorithm mechanisms 1934 to enablethe master controller to determine what power factor should be appliedfrom the inverters based on conditions of the grid. Remote controlalgorithms 1936 represent mechanisms used by master controller 1932 tocommunicate with the inverters.

It will be understood that each inverter 1912-1916 individually can beset to a particular power factor, and the cumulative effect of themultiple devices in coordination would be to provide conditioned andfiltered power at a particular power factor. While it is conceivablethat the inverters individually may operate at different power factors,and as a whole system provide power at a particular power factor, theremay be more efficiency in operating each inverter at the target powerdelivery conditions (power factor, voltage, and frequency). Oneadvantage to such an approach is that the interfacing of the invertersto grid 1950 through point B at meter 1940 should be simpler and moreefficient than if each inverter were operating at different settings.

With the configuration of system 1900, during an emergency the utilitycould remotely command all or some of the inverters in the farm toproduce a majority of reactive power. It will be understood that insystem 1900 there is no local load, but rather grid 1950 acts as aninfinite sink of power. The grid will take either active or reactivepower. Hence the utility can command the inverters to produce whatevermix of power they need to stabilize the grid voltage. Thus, control atthe various points A1, A2, . . . , AN, can affect the grid at points Band C, at least within a certain geographic region.

As described, power factor conditioning provides a mechanism for theselection of a mix of active and reactive power at the output (pointsA1-AN) of each inverter 1912-1916, and at the grid-tied electrical meter(point B and/or point C), automatically using software algorithm(s)embedded within each inverter. Additionally, system 1900 provides amechanism for the remote selection and establishment of such a mix overcommunication interfaces (e.g., an internet browser, telephone, radio orother manner of communications) using software protocols built into eachinverter. Additionally, system 1900 provides a mechanism for mastercontroller 1932 to control the desired mix of active and reactive poweremanating from one or more slave inverters, using either the automaticmechanism of each inverter and/or the remote communications mechanism.

FIGS. 20, 21, and 22 illustrate various mechanisms used to provide powerto loads and deliver excess power to an electrical grid. FIG. 20 focuseson the use of grid monitoring to identify the power factor at the grid,feeding the information to a single inverter, where internal algorithmsdetermine a preferred mix of active and reactive power. FIG. 21 focuseson the use of communication protocols over communication media orcommunication lines the internet, cell phone lines, or othercommunications medium to allow remote power factor setting. The remotecommunication may allow for utility control of the power factor setting,rather than owner control. Such control is possible in a configurationsuch as that of system 2100. FIG. 22 focuses on the use of a mastercontroller, which dictates a desired output mix to single inverters, orto groups of inverters. The master controller can act according to anautomatic mechanism relying on its internal software algorithms, or to aremote communications mechanism relying on remote communications.

FIG. 20 is a block diagram of an embodiment of a power factor feedbackmechanism. System 2000 illustrates source 2010 providing DC power toinverter 2020, which includes inversion processor 2022, inversioncontroller 2024, and software algorithm 2026. Power is delivered frominverter 2020 to load Z2002. System 2000 also illustrates monitoring ofpower factor at point B with power factor feedback 2032. Alternatively,monitoring could occur at point C beyond meter 2030 as well as at pointB.

Monitoring the power factor at either point B or point C allows softwarealgorithms 2026 (i.e., control logic) to compare the actual power factorwith the desired power factor, and thus self-regulate the output powerof inverter 2020 at point A. As shown above, by controlling the outputat point A, inverter 2020 moves the power factor of the grid-tiedconnection or the point of connection looking out to the grid toward avalue of best benefit. The best benefit may not always be a power factorof unity. As described above, the power factor may be best set at avalue based on power grid conditions as well as tariff conditions.Algorithm(s) 2026 may use a “best benefit” calculation that depends onthe currently applicable tariff, which may include any and all factorsthat the utility might require in such a tariff FIG. 21 is a blockdiagram of an embodiment of a communication system to control powerfactor remotely. System 2100 illustrates source 2110 providing DC powerto inverter 2120, which includes inversion processor 2122, inversioncontroller 2124, software algorithm 2126, and remote control mechanism2128. Power is delivered from inverter 2120 to load Z2102. Power fromgrid 2140 is measured at meter 2130. Power factor may be measured atpoint B (or some other point C) and provided to software algorithm 2126as power factor feedback 2132.

System 2100 also illustrates the use of remote communication 2162. Eachform of communication may use a different communication protocol. Remotecontrol 2128 may include support for one or multiple communicationmechanisms. Such mechanisms may include communication, for example, overthe internet by web browser 2152, by cell-phone or other mobileapplication 2154, by radio transmitter (by any signal in an RF band)2156, by home or community wireless systems (e.g., IEEE 802.1x systems)2158, via Telnet 2160 or other dial-up mechanism, or by anothercommunication mechanism. Such communication portals may feed commands,made at a location remote to load Z2102, to the power factor controllermechanisms of inverter 2120 (e.g., software algorithm 2126, inversioncontroller 2124, and inversion processor 2122). Inversion controller2124 changes the power factor at point A, which ultimately changes thepower factor at points B and C on grid 2140. The communication protocolsinclude two direction communications, allowing information on thecurrent power factor setting, either at point A, point B, and/or point Cto be made to the remote controller. In one embodiment, the remotecontroller makes the decisions of “best benefit” power factor settinginstead of allowing such a decision to be made locally, or to overridesuch a decision made locally.

FIG. 22 is a block diagram of an embodiment of a system that controlspower factor with a master/slave configuration. System 2200 includesmultiple inverters 2212-2216, each with an associated remote controlmechanism 2222-2226. Each inverter can provide a specific mix of activeand reactive power to deliver to grid 2250 through meter 2240. Eachinverter 2212-2216 is shown having an effective point A: A1, A2, . . . ,AN. It will be understood that in certain embodiments all these pointsmay be the same point. The output of all inverters is combined anddelivered to the grid.

Master controller 2232 sends commands to one or more individualinverters 2212-2216 of system 2200 using a remote communicationmechanism. Master controller 2232 controls the individual inverter“slaves” through a communication system via remote control 2222-2226. Inone embodiment, master controller 2232 applies its own internal softwarealgorithms 2234 to determine how to guide the behavior of the individualinverters, such illustrated in FIG. 19 above. Alternatively, mastercontroller 2232 may use its own communication channel(s) via remotecommunication algorithms 2236 to communicate with one or more remotelocations. In the case of remote communication, commands may appear inmaster controller 2232 over a communication portal, such as over theinternet by web browser 2252, by cell-phone or other mobile application2254, by radio transmitter 2256, by wireless systems 2258, via Telnet2260, or other type of interactive channel and protocol. Such commandsare forwarded by master controller 2232, after processing, to slaveinverters 2212-2216. The slave inverters then change the power factor atA accordingly, thus affecting the power factor at points B and C on grid2250.

FIG. 23 is a block diagram of an embodiment of a control process forpower factor control. The control process illustrated may beimplemented, for example, by software algorithms in an inverter or amaster controller, in accordance with what is described above.Comparison algorithm 2310 receives input about the time of day 2314,power currently available from connected power sources 2316, and tariffcharacteristics 2312. The comparison algorithm could be implemented astable lookups, as variable calculations, or in a state machine. Time ofday 2314 is determined by a clock input. Tariff characteristics 2312 areconfigured into the system to indicate the most current tariff in placefrom the utility company. The tariff characteristics could beimplemented as a set of rules or in a state machine. Power available2316 is determined by measuring output at the devices that make up thepower sources. The comparison generates a result that indicates a set ofconditions based on the tariff.

The comparison algorithm result is received at determination algorithm2320, which computes best benefit power factor 2330 based on thecomparison result and multiple other conditions or factors. Thecharacteristics of the tariff have associated best benefit criteria2322, which is a set of rules that is used to interpret an intersectionof the time of day, available power, and tariff characteristics.Determination algorithm 2320 also takes into consideration power factoras measured at the meter 2324 (either at points B or C). In oneembodiment, there is also the possibility of remotely controlling orinfluencing the process; thus, remote override 2326 is considered bydetermination algorithm to determine if a remote or external command orcontrol influences the determination.

In one embodiment, remote settings 2318 can be applied over remotecommunication channels as discussed above. Tariff settings can beconfigured and changed dynamically from a remote system. In addition tochanging tariff characteristics 2312, best benefit criteria 2322 canalso be changed or configured remotely.

The determination is implemented in the system by setting parametersthat affect the power factor of the system. Thus, the output of thedetermination algorithm can be parameters used to set or adjust settingson current system controls that produce the current power factor.Similar to how settings may be remotely influenced, the determinationprocess can also be remotely overridden. Overriding the process may bedone by commands or controls that cause the system to not implementpower factor changes computed by the determination algorithm, as well asby commands that override the settings computed by the determinationalgorithm.

As set forth in the claims below, in one embodiment, a method isimplemented that includes receiving, at a power converter, directcurrent (DC) power from a local power source, the local power source andthe power converter electrically located on a same side of a point ofconnection to a utility power grid as a local load tied to the powergrid, where the local load includes a consumer premises of the powergrid, converting with the power converter the DC power to alternatingcurrent (AC) power to deliver to the local load, conditioning a powerfactor of the AC power by controlling the phase of the generated currentwith respect to phase of the voltage of the power grid, and deliveringthe conditioned AC power on the local load side of the power grid.

The receiving may include receiving power from a metastable powersource, or receiving the power at a micro-inverter installed on theconsumer premises. A metastable local power source may include a solarpower source, a tidal power source, a wind power source, or a thermallycoupled heat source.

Conditioning the power factor may include receiving characteristic shapeand phase information about a target periodic waveform having a phasewith respect to an AC voltage of the power grid, generating an outputwaveform with output hardware, sampling the output waveform, comparingthe output waveform to a corresponding reference output waveform, thereference output waveform representing an ideal version of the targetperiodic waveform based on the received characteristic shape and phaseinformation, generating a feedback signal based on comparing the outputwaveform to the reference output waveform, and adjusting an operation ofthe output hardware at runtime based on the feedback signal, whereinadjusting the operation of the output hardware converges the outputwaveform toward the reference output waveform and phase.

Conditioning the power factor may further include conditioning the powerfactor by adjusting a phase of generated AC current with a table-basedphase adjustment, or conditioning the power factor of the generated ACcurrent based on conditions of the power grid. Conditioning based onconditions of the power grid may include measuring one or moreconditions of the power grid from the customer premises, receivingmeasurements from outside the customer premises, or receiving a remotecommunication from the other side of the point of connection indicatinga power factor adjustment and adjusting the power factor in response toreceiving the remote communication. Receiving remote communication mayinclude receiving a communication via internet, cellular, radio, or WiFiinterface.

Conditioning the power factor based on conditions of the power grid mayinclude receiving a communication from a master controller on the sameside of the point of connection indicating a power factor adjustment,and adjusting the power factor in response to receiving thecommunication. Conditioning the power factor may include degrading thepower factor away from unity responsive to conditions of the power grid.

Conditioning the power factor may include adjusting the power factor toapproximately unity or to approach unity. Conditioning the power factormay include conditioning the power factor of the generated AC currentbased on a best benefit analysis, including considering a power ratetariff set by a utility of the power grid.

Delivering the conditioned AC power may include delivering conditionedAC power to the power grid. The power may be delivered to a specificgeographic area, or to a neighbor load.

In an implementation of an inverter apparatus, the inverter may includeinput hardware to receive a direct current (DC) power from a local powersource, the local power source and the inverter electrically located ona same side of a point of connection to a utility power grid as a localload tied to the power grid, where the local load includes a consumerpremises of the power grid, inverter hardware to convert the DC power toalternating current (AC) power to deliver to the local load, powerfactor conditioning hardware to condition a power factor of the AC powerby controlling the phase of the generated current with respect to phaseof the voltage of the power grid, and output hardware to deliver theconditioned AC power on the local load side of the power grid.

The power factor conditioning hardware may include a software algorithmto locally determine power factor conditioning. The inverter may furtherinclude a remote control mechanism to receive a command from a remotedevice providing input for determining power factor conditioning.

In one embodiment, an implementation of power factor conditioning isperformed for an AC to DC converter, where the method may includereceiving, at an AC/DC power supply, alternating current (AC) power,conditioning a power factor of the AC power by controlling a phase ofcurrent of the AC power with respect to phase of an AC voltage of thepower supply, wherein controlling the phase includes adjusting the phaseof the current of the AC power to be in phase with the phase of the ACvoltage, converting the conditioned AC power into direct current (DC)power, and delivering the DC power to a load of the power supply.

Conditioning the power factor may include conditioning the power factorby adjusting a phase of AC current based on a table-based phaseadjustment.

Various operations or functions are described herein, which may bedescribed or defined as software code, instructions, configuration,and/or data. The content may be directly executable (“object” or“executable” form), source code, or difference code (“delta” or “patch”code). The software content of the embodiments described herein may beprovided via an article of manufacture with the content stored thereon,or via a method of operating a communication interface to send data viathe communication interface. A machine readable medium may cause amachine to perform the functions or operations described, and includesany mechanism that provides (i.e., stores and/or transmits) informationin a form accessible by a machine (e.g., computing device, electronicsystem), such as recordable/non-recordable media (e.g., read only memory(ROM), random access memory (RAM), magnetic disk storage media, opticalstorage media, flash memory devices, or other hardware storage media). Acommunication interface includes any mechanism that interfaces to any ofa hardwired, wireless, optical, medium to communicate to another device,such as a memory bus interface, a processor bus interface, an Internetconnection, or a disk controller. The communication interface can beconfigured by providing configuration parameters and/or sending signalsto prepare the communication interface to provide a data signaldescribing the software content. The communication interface can beaccessed via one or more commands or signals sent to the communicationinterface.

Various components described herein may be a means for performing theoperations or functions described. Each component described hereinincludes software, hardware, or a combination of these. The componentscan be implemented as software modules, hardware modules,special-purpose hardware (e.g., application specific hardware,application specific integrated circuits (ASICs), digital signalprocessors (DSPs), or other programmable devices), embedded controllers,or hardwired circuitry.

Besides what is described herein, various modifications may be made tothe disclosed embodiments and implementations of the invention withoutdeparting from their scope. Therefore, the illustrations and examplesherein should be construed in an illustrative, and not a restrictivesense. The scope of the invention should be measured solely by referenceto the claims that follow.

What is claimed is:
 1. A method comprising: receiving, at a powerconverter, direct current (DC) power from a local power source, thelocal power source and the power converter electrically located on asame side of a point of connection to a utility power grid as a localload tied to the power grid, where the local load includes a consumerpremises of the power grid; converting with the power converter the DCpower to alternating current (AC) power to deliver to the local load,including generating a reactive power component from the DC power; anddelivering the AC power on the local load side of the power grid.
 2. Themethod of claim 1, wherein generating the reactive power componentcomprises: generating an AC current waveform out of phase with respectto a voltage waveform off the grid, based on a table-based phaseadjustment.
 3. The method of claim 1, wherein generating the reactivepower component comprises: generating the reactive power component inresponse to detection of a reactive power need by the local load.
 4. Themethod of claim 1, wherein generating the reactive power componentfurther comprises: generating an output current waveform with outputhardware; sampling the output current waveform; comparing the outputcurrent waveform to a corresponding the reference output waveform;generating a feedback signal based on comparing the output currentwaveform to the reference output waveform; and adjusting an operation ofthe output hardware at runtime based on the feedback signal to convergethe output current waveform toward the reference output waveform andphase.
 5. A method comprising: receiving characteristic shape and phaseinformation about a target periodic waveform; generating an outputwaveform with output hardware; sampling the output waveform; comparingthe output waveform to a corresponding reference output waveform, thereference output waveform representing an ideal version of the targetperiodic waveform based on the received characteristic shape and phaseinformation; generating a feedback signal based on comparing the outputwaveform to the reference output waveform; and adjusting an operation ofthe output hardware at runtime based on the feedback signal, whereinadjusting the operation of the output hardware converges the outputwaveform toward the reference output waveform and phase.
 6. The methodof claim 5, wherein the output waveform and the reference outputwaveform comprise an output current waveform and a reference outputcurrent waveform, respectively.
 7. The method of claim 5, whereingenerating the output waveform comprises: generating the output waveformbased on a pulse width modulated base waveform, the pulse widthmodulated base waveform created from entries in a pulse width modulator(PWM) table.
 8. The method of claim 7, wherein adjusting the operationof the output hardware further comprises: dynamically adjusting one ormore entries in the PWM table during runtime based on the generatedfeedback signal.
 9. The method of claim 5, wherein sampling the outputwaveform and comparing the output waveform to the reference outputwaveform comprises: sampling and comparing point-by-point between thetwo waveforms.
 10. The method of claim 5, wherein comparing the outputwaveform to the reference output waveform comprises: precomputing a setof ideal sample points representing the reference output waveform priorto sampling the output waveform; and storing the precomputed samplepoints.
 11. The method of claim 5, wherein comparing the output waveformto the reference output waveform comprises: comparing a sample point ofthe output waveform to a corresponding reference setpoint with a PID(proportional-integral-derivative) controller.
 12. The method of claim5, wherein adjusting the operation of the output hardware furthercomprises: adjusting the operation of the output hardware to reduceharmonic distortion in the output waveform without performing a specificharmonic distortion analysis.
 13. The method of claim 5, furthercomprising: dynamically adjusting entries in a reference waveform tableduring runtime to dynamically adjust the reference output waveform. 14.The method of claim 5, further comprising: shifting the output waveformin phase dynamically with respect to the target periodic waveformwithout increasing harmonic distortion.
 15. A method comprising:receiving, at an AC/DC power supply, alternating current (AC) power;conditioning a power factor of the AC power by controlling a phase ofcurrent of the AC power with respect to phase of an AC voltage of thepower supply, wherein controlling the phase includes adjusting the phaseof the current of the AC power to be in phase with the phase of the ACvoltage; converting the conditioned AC power into direct current (DC)power; and delivering the DC power to a load of the power supply. 16.The method of claim 15, wherein conditioning the power factor furthercomprises: conditioning the power factor by adjusting a phase of ACcurrent based on a table-based phase adjustment.